1. Field of the Invention
The present invention relates to backlight technology and more particularly, to a low profile keyboard backlight module, which comprises a bottom membrane layer, a top membrane layer and an intermediate membrane layer sandwiched between the bottom membrane layer and the top membrane layer in a stack and having, a light-emitting layer embedded therein, lowering the overall thickness of the module and providing a waterproof effect.
2. Description of the Related Art
With fast development of the modern technology, many different kinds of electrical and electronic products have been created and widely used in our daily life, bringing comfort and convenience to people and improving the standard of living of the people. The jobs of word processing, photos and graphics editing, presentations, e-mail, Internet linking, and etc. are quite common in our everyday lives, making the application of computer products become more popular. In various electronic works through a computer system, one must input data through a keyboard, so that the host of the computer system can start processing according to the inputted data. Therefore, a computer keyboard has become an essential tool for the computer jobs. It is now the market trend to design computers and peripheral apparatuses having light, thin, short and small characteristics and enhanced functions, the overall thickness of a computer, more particularly, notebook computer, must be greatly reduced. In consequence, the thickness of computer display screens and keyboards must also be greatly reduced. Nowadays, low profile membrane keyboards have been widely used in various computer products to replace conventional mechanical keyboards. Further, a computer keyboard may have a light source mounted therein for emitting light to each key switch that is pressed by the user so that the user can clearly identify the location of the key that is duly pressed. A light-emitting keyboard structure generally comprises a mask layer, a light guide layer and a reflective layer arranged at different elevations under the keys, and a plurality of light-emitting diodes mounted in the circuit board of the light guide layer. The reflective layer is adapted to reflect the emitted light of the light-emitting diodes upwardly. The mask layer masks the reflected light in predetermined areas so that the reflected light can be concentrated and upwardly guided to each pressed key or the area around each pressed key. The mask layer, the light guide layer and the reflective layer constitute a backlight reflecting layer. Further, the mask layer has holes corresponding to the keys of the keyboard so that the reflective layer can reflect the light in the light guide layer toward the keys through the holes in the mast layer. However, a backlight module of this design has a certain thickness so that the light-emitting diodes can be mounted in the light guide layer between the mask layer and the reflective layer. The thickness of the backlight module cannot be further reduced for low profile application.
In order to reduce the height of a keyboard backlight module, some manufacturers adopt an electroluminescent lamp as a light source for keyboard backlight module. By means of applying an electric field to the electroluminescent lamp in the keyboard backlight module, the electroluminescent lamp is energized to emit light. FIG. 6 illustrates a keyboard backlight module according to the prior art. According to this design, the keyboard backlight module comprises a key switch layer A, an electroluminescent layer B, and a substrate C. The key switch layer A and the electroluminescent layer B are respectively mounted at opposing top and bottom surfaces of the substrate C. The substrate C can be a transparent panel member or a stainless steel panel with holes therein. When the electroluminescent layer B is energized, it emits light through the substrate C toward the key switch layer A. However, the fabrication and installation of this design of keyboard backlight module are complicated. Further, this design of keyboard backlight module still has a certain thickness. FIG. 7 illustrates another design of keyboard backlight module according to the prior art. According to this design, the keyboard backlight module comprises an integrated key switch and electroluminescent layer combination D and a substrate C. The integrated key switch and electroluminescent layer combination D comprises an insulative layer, a conducting layer, a light-emitting layer and a lead wire layer D1 arranged together through lamination with the lead wire layer D1 exposed to the outside of the integrated key switch and electroluminescent layer combination D. In actual application, the lead wire layer D1 of the integrated key switch and electroluminescent layer combination D can easily be affected with damp, leading to waterproofing failure. An improvement is necessary.
Therefore, it is desirable to provide a keyboard backlight module that has a low profile and is practical for use in an electronic product having light, thin, short and small characteristics and can effectively protect the conducting components and circuits against damp and mould.